Field
The disclosure relates to an oscillator arrangement and a calibration unit for calibrating an oscillator, in particular an oscillator for a universal serial bus, universal serial bus (USB) device and to a method for calibrating such an oscillator.
Description of the Art
The USB standard allows plug-and-play interconnection of USB devices to a USB host, such as a computer, a tablet or a smartphone. Such USB devices can be as small as a memory drive, a mouse, a webcam, a microphone or the like. Therefore, USB became ubiquitous as an interconnecting standard, allowing for a high communication speed.
However, a USB device commonly requires an oscillator for example for generating a clock that synchronizes data traffic with the USB host. This clock may for example by required to satisfy a high accuracy. For example, according to USB 2.0 standard, an accuracy of ±500 ppm may be required.
For example due to fabrication process deviations and/or temperature variations, it may be necessary for a fully integrated implementation of such an oscillator to employ a complicated calibration methodology. Conventional calibrated oscillators may require for example calibration at a manufacturing factory using for example measurements at multiple temperatures, which may lead to high costs.
A solution adopted has been to use an oscillator with an external precise resonator, for example a quartz or a ceramic resonator. However, these are commonly bulky external components occupying area and increasing the costs, which may be a serious problem for low cost and miniature USB devices. In addition, the external resonator may require two input/output pins for an off-chip connection. Since many chips are input/output limited, using an external resonator may add additional costs.
Consequently it is desirable to provide an improved concept for calibrating an oscillator, in particular for calibrating an oscillator of a USB device. This objective is achieved by the subject-matter of the independent claims. Further embodiments and implementations are subject-matter of the dependent claims.